The present invention relates to a cleaning solution for electronic materials. In particular, the present invention involves wet cleaning where impurities and especially particulate matter are removed from the surface of electronic materials. The cleaning solution is effective at room temperature using low concentrations of dissolved chemicals. The present invention includes a method for cleaning electronic materials.
Removing particulate matter, or particles, from the surfaces of electronic materials such as semiconductor silicon substrates, liquid crystal glass substrates, and photomask quartz substrates, is extremely important in order to prevent defective products. Traditionally, an aqueous solution of a mixture of ammonia and hydrogen peroxide is used with heat to achieve this objective. This method is called APM cleaning. The standard mixing ratio of the chemicals used in APM cleaning is a solution of aqueous ammonia (29% by weight), aqueous hydrogen peroxide (30% by weight), and water in a 1:1:5 ratio. Generally, washing takes place at a temperature of around 80xc2x0 C. The APM cleaning method is extremely effective in removing particles. However, the APM method has several problems. Since a high concentration of high purity chemicals is used, a great deal of ultrapure water is needed for the rinse after cleaning. Ultrapure water has a resistivity less than 16Mxcexa9 and less than 10 xcexcg/l total organic carbon. The high demand for ultrapure water results in excessive waste water processing. In addition, the APM method requires a mechanism for heating and temperature adjustment. This generates chemical contaminated steam, requiring an air pollution control system for removing contamination from the steam. The required local exhaust ventilation, air pollution control devices, and replacement of exhausted air with tempered fresh air, becomes very costly.
A number of methods have been investigated to overcome these disadvantages without losing the particle removal effect. For example, one method uses several-fold dilutions of the chemicals of the prior art, while the temperature is maintained at approximately 40xc2x0 C., or ambient temperature. This is used in conjunction with ultrasonic vibrations. This improvement is based on the APM method of the prior art. Although this method is easily implemented, and may be adapted for use in a mass production factory, the improvement over the disadvantages indicated above is not significant.
A cleaning solution for electronic materials is sought that uses low concentrations of chemicals and is effective at room temperature.
In light of the above, it is an object of the present invention to provide a cleaning solution for electronic materials which overcomes the limitations of the prior art.
The present inventors have discovered, through intensive research, that dissolving oxygen gas at a concentration greater than atmospheric saturation concentration, into water containing a low concentration of ammonia and hydrogen peroxide, results in a cleaning solution that is extremely effective in removing particles adhering to the surface of electronics material. Atmospheric saturation concentration is the concentration of gas dissolved in water when it is in equilibrium with the atmosphere. The atmospheric saturation concentration of oxygen gas fluctuates with temperature. At low temperatures, the atmospheric saturation concentration becomes higher, and at high temperatures, it becomes lower. At 20-25xc2x0 C., it is approximately 8-9 mg/liters.
It was also discovered that dissolving reducing agents into water containing low concentrations of ammonia and hydrogen peroxide results in a cleaning solution that is extremely effective in removing particles adhered to the surface of electronics material. The present invention is based on these findings.
It is an object of the present invention to provide a cleaning solution for electronic materials that removes impurities, especially particles, from the surface of electronic materials during wet cleaning, cleans effectively at room temperature, and requires only a low concentration of dissolved chemicals.
It is a further object of the present invention to provide a cleaning solution for electronic materials that conserves resources, is environmentally safe, and is easily implemented, even at mass production facilities.
It is a further object of the present invention to provide a method using such a cleaning solution that is suitable for mass production facilities.
Briefly stated, the present invention provides a cleaning solution for electronic materials which includes dissolved oxygen gas at a concentration greater than atmospheric saturation concentration, 0.1-10,000 mg/liter of ammonia and 0.1-10,000 mg/liter of hydrogen peroxide.
According to another embodiment of the present invention, a cleaning solution for electronic materials is provided including from about 0.00005 to 1 weight percent of a reducing agent, from about 0.1-10,000 mg/liter of ammonia and about 0.1-10,000 mg/liter of hydrogen peroxide.
According to an embodiment of the present invention, a method of cleaning electronic materials is provided that includes dissolving oxygen gas into a source water to a predetermined concentration in excess of atmospheric saturation concentration, adding from about 0.1 mg/liter to about 10,000 mg/liter of ammonia to the source water; and adding from about 0.1 mg/liter to about 10,000 mg/liter of hydrogen peroxide to the source water, to produce a cleaning solution.
According to another embodiment of the present invention, a method of cleaning electronic materials is provided that includes adding at least one reducing agent to a source water to a predetermined concentration from about 0.00005 to 1 weight percent, adding from about 0.1 mg/liter to about 10,000 mg/liter of ammonia to the source water, and adding from about 0.1 mg/liter to about 10,000 mg/liter of hydrogen peroxide to the source water, to produce a cleaning solution.
According to another embodiment of the present invention, a method for cleaning electronic materials includes dissolving oxygen gas in a source water at a predetermined concentration greater than atmospheric saturation concentration, adding ammonia to the source water at a predetermined concentration from about 0.1 mg/liter to about 10,000 mg/liter from an ammonia supply point, adding hydrogen peroxide to the source water at a predetermined concentration from about 0.1 mg/liter to about 10,000 mg/liter from a hydrogen peroxide supply point to form a cleaning solution, storing the cleaning solution in a storage container, measuring the flow rates of ammonia from the ammonia source point and of hydrogen peroxide from the hydrogen peroxide supply point, adjusting the flow rates of ammonia and hydrogen peroxide from the source points to maintain a constant concentration of cleaning solution in the storage container, transporting the cleaning solution to at least one use point, and cleaning the electronic materials with the cleaning solution at the at least one use point.
According to another embodiment of the present invention, a method for cleaning electronic materials includes forming a cleaning solution by adding at least one reducing agent into a source water at a predetermined concentration from about 0.00005 weight percent to about 1 weight percent, adding ammonia to the source water at a predetermined concentration from about 0.1 mg/liter to about 10,000 mg/liter from an ammonia supply point, adding hydrogen peroxide to the source water at a predetermined concentration from about 0.1 mg/liter to about 10,000 mg/liter from a hydrogen peroxide supply point to form a cleaning solution, storing the cleaning solution in a storage container, measuring the flow rates of ammonia from the ammonia source point and of hydrogen peroxide from the hydrogen peroxide supply point, adjusting the flow rates of ammonia and hydrogen peroxide from their respective source points to maintain a constant concentration of cleaning solution in the storage container, transporting the cleaning solution to at least one use point, and cleaning electronic materials with the cleaning solution at the at least one use point.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.